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The occurrence of a penis in female gastropods has commonly been accepted as an indicator of tributyltin (TBT) pollution. During the surveys performed in Patagonian waters between 2002 and 2010, individuals ofBuccinanops deformiswith a short penis and an external vas deferens were initially considered as showing imposex. Doubt arose when different manifestations of the phenomenon were identified at the two sites with the densest populations of the species (San Antonio Bay, SAB, and Villarino). This led us to search at both locations for: (a) histological confirmation of sex, (b) butyltin measurements in sediments and snail tissues, and (c) incidence of trematode infestation. We found that both populations have individuals with a short penis. While all the inspected individuals from SAB were histologically identified as females (imposex), those from Villarino were identified as males. Trematodes were absent in individuals from SAB and showed very low prevalence in those from Villarino, with metacercariae found in the digestive gland. In snail tissues, butyltins were found mainly in the form of dibutyltin (DBT) in SAB and at negligible levels in Villarino. In sediments, butyltins were found only in the form of TBT, at higher levels in SAB than in Villarino. Thus, it became clear that our finding of a short penis is a manifestation of imposex on females from SAB related to the high TBT levels, whereas in Villarino it is a male trait, which is not related to TBT or a trematode infestation but may be a Dumpton syndrome-like abnormality. [ABSTRACT FROM AUTHOR]

The force required to dislodge mussels from the substrate is known as attachment strength. This feature has been mostly studied in mytilids inhabiting the intertidal of consolidated rocky substrates, whereas it has been less studied in sedimentary substrates. The aim of this study was to evaluate the attachment strength and the number of byssal threads of Brachidontes rodriguezii in two sites with mobile substrates in San Antonio Bay, Argentina [Punta Verde (PV) and Punta Delgado (PD)]. PV has relatively higher current velocities and coarser grain size than PD. Along coastal line transects at two different levels of the mid-intertidal of each site, the attachment strength was measured. The number of byssal threads in collected mytilids and the weight of the sediment adhered to them were recorded in the lab. The attachment strength, the number of byssal threads and the sediment adhered to the byssus differed significantly between levels and sites. Mytilids from the mid-level of both sites where the density was relatively lower, had a significantly greater number of byssal threads and higher weight of sediment adhered. This study reveals that a high amount of coarse sediment adhered to the byssus affects the attachment strength of B. rodriguezii in ecosystems relative to unstable substrates. We underline the importance of mobile substrates in understanding attachment features (attachment strength and byssal threads) of mytilids in this unstable ecosystem. [ABSTRACT FROM PUBLISHER]

Ecosystem engineers can modify the environment, affecting the associated community. Studies of mussels as ecosystem engineers have been conducted mostly in the rocky intertidal zone, while those in sedimentary intertidals have been relatively scarce. The present study assessed the effect of varying densities of Brachidontes rodriguezii on local environmental variables (substrate weight, water content, organic matter, weight of sediments adhering to mussel byssus) and ecological attributes of the associated community (richness, abundance, diversity, evenness, and assemblage structure) at different intertidal levels, sites, and seasons, in a mixed-sediment intertidal region in San Antonio Bay (Patagonia, Argentina). We performed two independent manipulative field experiments at low and mid intertidal levels at two sites -Punta Verde (PV), with relatively higher current velocities and coarser grain sizes than Punta Delgado (PD)- in both winter and summer. Manipulative experiments consisted in reducing mussel density to 50% in the low intertidal and increasing that density to up to 100% in the mid zone. We hypothesized that local environmental variables and ecological attributes associated with B. rodriguezii depended on mussel density. The reduction in B. rodriguezii density increased the evenness and reduced the abundance at PD plus reduced the richness at PV. Also, when reducing mussel density, the assemblage structure differed in water content and organic matter at both sites between treatments and seasons. The sediment weight adhering to mussel byssus in PD and substrate weight in PV were the best descriptors of the assemblages. The increase in mussel density, however, produced a weak effect on the ecological attributes of the community, and the assemblage structure did not correlate with the environmental variables considered. Our results demonstrated a stronger engineering effect of B. rodriguezii at reduced, but not increased, mussel density. This study revealed that the ecological attributes associated with B. rodriguezii both were density-dependent and varied with sites along the year in mixed-sediment intertidal zones. • Manipulative experiments showed an engineering effect of the mussel B. rodriguezii. • Increasing and reducing the mussel-density modified the local environmental variables. • Manipulation of the mussel density affected the evenness, abundance and richness. • This effect was stronger in the low than in the mid-intertidal level in both sites. • The assemblage structure was explained by some environmental variables. [ABSTRACT FROM AUTHOR]